This application is based upon and claims the benefit of priority from the prior Japanese Patent Applications No. 11-089173, filed Mar. 30, 1999; and No. 11-089175, filed Mar. 30, 1999, the entire contents of which are incorporated herein by reference.
This invention relates to a nonaqueous electrolyte secondary battery.
At present, a thin lithium ion secondary battery is commercialized as a nonaqueous electrolyte secondary battery which is adapted to be used in a portable equipment such as a portable telephone. This battery comprises a positive electrode containing lithium cobalt oxide (LiCoO2), a negative electrode containing a graphite material or carbonaceous material, a liquid nonaqueous electrolyte comprising an organic solvent containing a lithium salt dissolved therein, a separator consisting of a porous film, and a jacket consisting of a cylindrical or rectangular metallic can.
Although it is now desired to make the battery thinner or lighter in conformity with an increasing trend for the miniaturization and thinning of a portable equipment, it has been difficult to realize a thin lithium ion secondary battery provided with the aforementioned liquid nonaqueous electrolyte and a metallic can and having a thickness of not more than 4 mm.
Meanwhile, another type of lithium ion secondary battery has been proposed and studied for further development thereof, this lithium ion secondary battery comprising an electrode group consisting of a positive electrode, a negative electrode, and a polymer electrolyte layer interposed between the positive electrode and the negative electrode, an electrolyte consisting of a polymer electrolyte, and a jacket for housing the aforementioned electrode group. It is possible, in the case of this secondary battery, to ensure the adherence of the positive and negative electrodes to the polymer electrolyte layer even if the thickness of the jacket is reduced. As a result, it is possible to employ a laminate film consisting of a thin metallic layer and a polymer film as a material for the jacket. The polymer electrolyte is composed of a gel-like polymer in which a nonaqueous electrolyte is held.
This secondary battery however is accompanied with a problem that since this secondary battery is relatively large impedance at the interface of electrode and relatively low in lithium ionic conductivity as compared with the aforementioned lithium ion secondary battery provided with a liquid nonaqueous electrolyte, this secondary battery is poor in volume energy density as well as in large discharge characteristic as compared with the aforementioned lithium ion secondary battery provided with a liquid nonaqueous electrolyte.
In view of the aforementioned circumstances, the following proposals have been made so far for thinning the lithium ion secondary battery provided with a liquid nonaqueous electrolyte.
For example, Japanese Patent Disclosure (Kokai) H10-177865 discloses a lithium ion secondary battery including a positive electrode, a negative electrode, a separator having opposed surfaces holding an electrolyte, and an adhesive resin layer which is made from a mixed phase of an electrolyte phase, a polymer gel phase containing an electrolyte, and a polymer solid phase and adheres the positive and negative electrodes to the opposing surfaces of the separator.
Further, Japanese Patent Disclosure (Kokai) H10-189054 discloses in the claims thereof a method of manufacturing a lithium ion secondary battery comprising the steps of; coating a separator with a binder resin solution prepared by dissolving polyvinylidene fluoride as a main component in a solvent, putting an electrode on this separator and drying these materials, as they are adhered to each other, to evaporate the solvent and thereby form a battery stacked body, and impregnating this battery stacked body with an electrolyte. Furthermore, Japanese Patent Disclosure (Kokai) H10-172606 discloses in the claims thereof a lithium ion secondary battery including a positive electrode, a negative electrode, a separator interposed between the positive electrode and the negative electrode and holding an electrolyte containing lithium ion, and a porous adhesive resin layer holding the electrolyte and adhering the positive electrode, the negative electrode and the separator. The secondary battery disclosed in Japanese Patent Disclosure (Kokai) H10-172606 is constructed such that the bonding strength between the layer of positive electrode and the separator is the same with or higher than the bonding strength between the layer of positive electrode and the positive electrode collector, and that the bonding strength between the layer of negative electrode and the separator is the same with or higher than the bonding strength between the layer of negative electrode and the negative electrode collector.
However, these lithium ion secondary batteries disclosed in these publications are all accompanied with the problem that since the internal impedance thereof tends to become higher, thereby deteriorating the charge/discharge cycle life (which may be referred to hereinafter as cycle life).
Accordingly, an object of the present invention is to provide a secondary battery which includes a light-weight and thin jacket and is excellent in cycle life.
Another object of this invention is to provide a secondary battery exhibiting an enhanced thermal stability and an improved safety.
A further object of this invention is to provide a secondary battery which includes a light-weight and thin jacket and is excellent in resistance against an external shock.
Namely, according to the present invention, there is provided a secondary battery comprising an electrode group comprising a positive electrode, a negative electrode having a negative electrode collector and a negative electrode layer held to the collector, and a separator interposed between the positive electrode and the negative electrode layer; a nonaqueous electrolyte held by the electrode group; and a jacket housing the electrode group and having a thickness of not more than 0.3 mm,
wherein the positive electrode, the negative electrode and the separator are formed integral, and the peeling strength between the negative electrode layer and the separator is lower than the peeling strength between the negative electrode layer and the negative electrode collector.
According to the present invention, there is also provided a secondary battery comprising an electrode group comprising a positive electrode having a positive electrode collector and a positive electrode layer held to the positive electrode collector, a negative electrode having a negative electrode collector and a negative electrode layer held to the negative electrode collector, and a separator interposed between the positive electrode layer and the negative electrode layer; a nonaqueous electrolyte held by the electrode group; and a jacket housing the electrode group and having a thickness of not more than 0.3 mm,
wherein the positive electrode, the negative electrode and the separator are formed integral, and the peeling strength between the positive electrode layer and the separator is lower than the peeling strength between the positive electrode layer and the positive electrode collector, while the peeling strength between the negative electrode layer and the separator is lower than the peeling strength between the negative electrode layer and the negative electrode collector.
According to the present invention, there is also provided a secondary battery comprising an electrode group comprising a positive electrode, a negative electrode having a negative electrode collector and a negative electrode layer held to the negative electrode collector, and a separator interposed between the positive electrode and the negative electrode layer; a nonaqueous electrolyte held in the electrode group; and a jacket housing the electrode group and having a thickness of not more than 0.3 mm,
wherein the positive electrode, the negative electrode and the separator are formed integral; the peeling strength between the negative electrode layer and the separator is lower than the peeling strength between the negative electrode layer and the negative electrode collector; the nonaqueous electrolyte contains a solution prepared by dissolving a solute in a nonaqueous solvent, the solution having a viscosity of 3 cp to 20 cp at a temperature of 20xc2x0 C.
According to the present invention, there is also provided a secondary battery comprising an electrode group comprising a positive electrode having a positive electrode collector and a positive electrode layer held to the positive electrode collector, a negative electrode having a negative electrode collector and a negative electrode layer held to the negative electrode collector, and a separator interposed between the positive electrode layer and the negative electrode layer; a nonaqueous electrolyte held in the electrode group; and a jacket housing the electrode group and having a thickness of not more than 0.3 mm,
wherein the positive electrode, the negative electrode and the separator are formed integral, the peeling strength between the positive electrode layer and the separator is lower than the peeling strength between the positive electrode layer and positive electrode collector, while the peeling strength between the negative electrode layer and the separator is lower than the peeling strength between the negative electrode layer and the negative electrode collector; the nonaqueous electrolyte contains a solution prepared by dissolving a solute in a nonaqueous solvent, the solution having a viscosity of 3 cp to 20 cp at a temperature of 20xc2x0 C.
According to the present invention, there is further provided a secondary battery comprising an electrode group comprising a positive electrode, a negative electrode having a negative electrode collector and a negative electrode layer held to the collector, and a separator interposed between the positive electrode and the negative electrode layer; a nonaqueous electrolyte held by the electrode group; and a jacket housing the electrode group, the jacket being made of a sheet having d thickness of not more than 0.5 mm and including a resin layer,
wherein the positive electrode, the negative electrode and the separator are formed integral, and the peeling strength between the negative electrode layer and the separator is lower than the peeling strength between the negative electrode layer and the negative electrode collector.
According to the present invention, there is also provided a secondary battery comprising an electrode group comprising a positive electrode, a negative electrode having a negative electrode collector and a negative electrode layer held to the negative electrode collector, and a separator interposed between the positive electrode and the negative electrode layer; a nonaqueous electrolyte held in the electrode group; and a jacket housing the electrode group, the jacket being made of a sheet having a thickness of not more than 0.5 mm and including a resin layer,
wherein the positive electrode, the negative electrode and the separator are formed integral; the peeling strength between the negative electrode layer and the separator is lower than the peeling strength between the negative electrode layer and the negative electrode collector; the nonaqueous electrolyte contains a solution prepared by dissolving a solute in a nonaqueous solvent, the solution having a viscosity of 3 cp to 20 cp at a temperature of 20xc2x0 C.
According to the present invention, there is further provided a secondary battery comprising an electrode group of flattened configuration which comprises a positive electrode having a positive electrode collector and a positive electrode layer held to the positive electrode collector, a negative electrode, and a separator interposed between the positive electrode and the negative electrode; a liquid nonaqueous electrolyte impregnated in the electrode group; and a jacket housing the electrode group and having a thickness of not more than 0.3 mm,
wherein the electrode group has a couple of maximum areas, at least one of which is occupied by the positive electrode collector.
According to the present invention, there is further provided a secondary battery comprising an electrode group of flattened configuration which comprises a positive electrode having a positive electrode collector and a positive electrode layer held to the positive electrode collector, a negative electrode, and a separator interposed between the positive electrode and the negative electrode; a liquid nonaqueous electrolyte impregnated in the electrode group; and a jacket housing the electrode group, the jacket being made of a sheet having a thickness of not more than 0.5 mm and including a resin layer,
wherein the electrode group has a couple of maximum areas, at least one of which is occupied by the positive electrode collector.
According to the present invention, there is further provided a secondary battery comprising an electrode group of flattened configuration which comprises a positive electrode, a negative electrode, and a separator interposed between the positive electrode and the negative electrode; a liquid nonaqueous electrolyte impregnated in the electrode group; and a jacket housing the electrode group and having a thickness of not more than 0.3 mm,
wherein the electrode group has a couple of maximum areas, each area is occupied by the separator.
According to the present invention, there is further provided a secondary battery comprising an electrode group of flattened configuration which comprises a positive electrode, a negative electrode, and a separator interposed between the positive electrode and the negative electrode; a liquid nonaqueous electrolyte impregnated in the electrode group; and a jacket housing the electrode group, the jacket being made of a sheet having a thickness of not more than 0.5 mm and including a resin layer,
wherein the electrode group has a couple of maximum areas, each area is occupied by the separator.
According to the present invention, there is further provided a secondary battery comprising an electrode group of flattened configuration which comprises a positive electrode, a negative electrode, and a separator interposed between the positive electrode and the negative electrode; a liquid nonaqueous electrolyte impregnated in the electrode group; and a jacket housing the electrode group and having a thickness of not more than 0.3 mm,
wherein the electrode group has a couple of maximum areas, and an insulating protective sheet is disposed to bridge the couple of maximum areas.
According to the present invention, there is further provided a secondary battery comprising an electrode group of flattened configuration which comprises a positive electrode, a negative electrode, and a separator interposed between the positive electrode and the negative electrode; a liquid. nonaqueous electrolyte impregnated in the electrode group; and a jacket housing the electrode group, the jacket being made of a sheet having a thickness of not more than 0.5 mm and including a resin layer,
wherein the electrode group has a couple of maximum areas, and an insulating protective sheet is disposed to bridge the couple of maximum areas.
The flattened configuration of the electrode group is preferably the one which can be obtained by spirally winding the positive electrode and the negative electrode with the separator being interposed therebetween and compressing the spiral in the direction of the diameter; the one which can be obtained by folding a laminate composed of the positive electrode, the negative electrode and the separator once or a plurality times; or the one which can be obtained by laminating the positive electrode, the negative electrode and the separator. Also, the flattened configuration of the electrode group is preferably the one which can be obtained by spirally winding the positive electrode and the negative electrode with the separator being interposed therebetween in a flattened shape.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.